div {
  background: #58a;
  background: linear-gradient(135deg, transparent 15px, #58a 0) top left, linear-gradient(225deg, transparent 5px, #58a 0) top right, linear-gradient(-45deg, transparent 15px, #58a 0) bottom right, linear-gradient(45deg, transparent 5px, #58a 0) bottom left;
  background-size: 50% 50%;
  background-repeat: no-repeat;
}
